Recently, attention has been paid to conservation of global environment and thus the prevention of global warming (CO2 reduction) has been demanded. For the CO2 reduction, each automobile manufacturer has been pursuing improvement of fuel efficiency in gasoline-powered vehicles and development of fuel-efficient diesel-powered vehicles.
As a method for improving fuel efficiency, weight saving is aimed at by changing the material of an engine block from cast iron to an aluminum material having a small specific gravity or by thinning the wall of the engine block. However, as a trade-off of the weight saving, a load on the engine block increases and hence vibration during engine running and strain deformation are generated to frequently result in occurrence of problems such as insufficient sealing.
On the one hand, the improvement of fuel efficiency has been pursued through increase of combustion pressure in the engine but the load on the engine block more increases and furthermore thermal resistance is also required.
In order to solve the above problems, hitherto, a fastening force is increased to restrict the movement of the engine block, thereby reducing the vibration and the strain deformation. For example, the problems are coped with through increase in fastening axial force with bolts, increase in bead height of the gasket, change in laminated structure of the gasket, and the like (see Patent Documents 1 and 2).
Patent Document 1: Japanese Patent No. 3840475
Patent Document 2: Japanese Patent No. 3620685